Patent Application
20150160254
1. Field of the Invention
The present disclosure relates to sensors, and more particularly to inductive contactless sensors for measuring rotational speed.
2. Description of Related Art
Induction-based sensor technology uses sensing coils that are made of copper traces printed on electronic printed circuit board. This type of sensor is capable of measuring the relative position between a sensing printed circuit and a position target without being in physical contact with it. This technology is outlined for various applications in U.S. Pat. Nos. 6,534,970 and 8,129,985, each of which is incorporated by reference in its entirety. This type of technology has been widely used for position sensing, but has not been often used to measure speed of a target.
Various sensor assemblies for measuring the rotational speed of an object are known in the art. In many conventional applications, the sensor system is either positioned in contact with the object to be measured, or is a non-contact system, e.g., with electromagnetic wound coils, magnet systems, or optical solutions. These systems have many disadvantages, including being expensive, bulky, heavy, or sensitive to noise introduced in harsh operating environments such as those having mechanical vibrations and variable temperatures. These systems are also subject to other sources of error including noise and signal interference associated with mounting analog signals around other sources of electromagnetic interference.
Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is a need in the art for implementing less expensive, smaller sized, and lighter weight devices with higher accuracy and better linearity for measuring rotational speed and communicating the output in a more robust digital signal that is more resistant to noise and electromagnetic interference. There is also a need to use less complex means to adopt advanced networking and wireless communication systems. The present disclosure provides a solution for such implementation.
An inductive rotational speed sensor assembly includes, inter alia, a first printed circuit board (PCB) including a transmitter coil and a receiver coil separate from the transmitter coil. The transmitter coil is configured to convert a high frequency alternating electrical input (e.g., in the multiple mega-cycles per second range) into an electromagnetic signal, e.g., an alternating magnetic field. A second PCB is operatively connected to (e.g., electromagnetically coupled to) the first PCB. In particular, the second PCB couples the electromagnetic signal coming from the transmitter coil of the first PCB with the receiver coil of the first PCB through a resonant circuit coil in series with a matching capacitor. The coupling factor between transmitter and receiver coils through the resonant circuit coil of the target second PCB in between varies with position, creating a signal in the receiver coil that is modulated with target position. This position modulated receive signal will have peaks and valleys alternating with target physical rotation. The frequency of change of these peaks and valleys is an indication of a target rotational speed.
In certain embodiments, the resonance and/or the receiver coils are non-axisymmetric relative to an axis of rotation defined by relative rotation of the first PCB and the second PCB. The receiver coil of the first PCB can include additional receiver windings to detect a rotational speed with increased precision and the receiver windings can be designed with increased number of poles to be able to measure rotation at much lower speeds. Similarly, the second PCB (target) can include at least one loop or variations of additional coil loops for increased sensing precision at lower rotational speeds. By increasing the windings or coil loops, target circuit resonance is introduced to further increase coupling and create a more robust receive signal at those frequencies.
In accordance with certain embodiments, the transmitter coil is positioned along an outer perimeter of the first PCB. The transmitter coil can also be positioned at an interior portion of the first PCB, as long as the location will provide the needed coupling with the resonant circuit coil. The first PCB can include a sequence of filters, signal amplifiers, and pulse counting circuit that are operatively connected to the receiver coil. This pulse count is directly proportional to the target rotational speed and can be translated with little calibration to speed indicating output.
A method of converting an electrical signal to a rotational speed includes first converting an alternating electrical input to an alternating magnetic field with a transmitter winding of a first PCB; receiving the alternating magnetic field with a resonance winding of a second PCB rotating relative to the first PCB; emitting a modulating position signal with the resonance winding of the second PCB; receiving the modulating position signal with a receiver winding of the first PCB; and outputting a signal indicative of rotational speed from the first PCB.
The method can include calculating the rotational speed from consecutive peaks created by constructive interference in the outputted signal. The rotational speed can be calculated using the time between consecutive peaks of the outputted signal. The method can also include converting the outputted signal to an angular speed using the equation ω=360°/nT, where ω is the angular speed in degrees per second, n is the number of receiver pairs of magnetic poles in the receiver coil on the first PCB, and T is the period of the output signal.
These and other features of the systems and methods of the subject disclosure will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings.
So that those skilled in the art to which the subject disclosure appertains will readily understand how to make and use the devices and methods of the subject disclosure without undue experimentation, preferred embodiments thereof will be described in detail herein below with reference to certain figures, wherein:
Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of the sensor assembly in accordance with the disclosure is shown in
Induction based rotational speed sensing in accordance with the disclosure can use electromagnetic coils made out of copper traces on a Printed Circuit Board (PCB). This sensor includes two adjacent PCBs separated by a nominally designed distance. The first PCB holds a high frequency electromagnetic field generator coil called the excitation or transmitter coil in addition to the sensing winding, also referred to as the receiver coil. The second PCB holds a resonator coil, also referred to as the target. The transmitter coil is energized with a high frequency alternating current input signal. This signal electromagnetically couples to the resonant target coil which in turn couples back to the receiver coil depending on the coil-to-coil alignment, which is a function of the angle between the imaginary central axes of the resonant target and receiver windings. As a result, when the target on the second PCB rotates relative to the first PCB, the receiver coil will receive a signal which amplitude is modulated by the target and receiver coil alignment to misalignment variation sequence as the target rotates on around its full axes. A series of signal pulses separated by a time period that is inversely proportional to the angular speed of the target is consequently generated in the receive coil signal. A circuit including one or more of a power supply, excitation signal generator, carrier demodulation circuit, a filter/amplifier combination, a comparator, and a high frequency clock counter can be used to detect the frequency of the consecutive electric pulses to determine the angular speed of the target.
As shown in
The transmitter coil 12 is positioned along an outer perimeter of the first PCB 10 but can also be placed in an interior portion as long as the location will provide the needed coupling with the resonant target coil 25. The first PCB 10 also includes a sequence of filters 16, signal amplifiers 17, and pulse counting circuit 18, which are operatively connected to the receiver windings 15, 15A for determining rotation speeds based on the signals from 15, 15A. The second PCB 20 also includes a capacitor 27 connected in series therewith for created a resonator. The resonator circuit provides a stronger signal in the resonant target coil 25 for better coupling to the receiver coil 15, enhanced output signal, and better signal to noise ratio.
A method of converting an electrical signal to a rotational speed is provided in the present disclosure using the sensor assembly of
The equation ω=360°/nT can be used to calculate an angular speed, where ω is the angular speed in degrees per second, n is the number of receiver windings pair of poles on the first PCB 10, and T is the period of the output signal 200. The accuracy of the calculated rotational speed can be improved by demodulating, filtering, and amplifying the raw electrical signal, shown in
The methods and systems of the present disclosure, as described above and shown in the drawings, provide for a sensor assembly that uses inductive based coils printed on electronic PCBs to effectively measure rotational speed, thereby providing performance, cost, size, weight, power, and reliability advantages over traditional sensors. While the apparatus and methods of the subject disclosure have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the spirit and scope of the subject disclosure.
This application claims priority to U.S. Provisional Patent Application No. 61/912,709 filed Dec. 6, 2013, which is incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61912709 | Dec 2013 | US |
